Preparation of synthetic rubber



Patented Sept. 11, 1945 vB. F. Goodrich Company,

New York, N. Y., a

corporation of New York No Drawing. Application September 27, 1941,

' Serial No. 412,680

12 Claims.

This invention relates'to the .preparation of synthetic rubber and particularly to the preparation of rubber-like materials by the emulsion polymerization of a mixture containing at least two butadiene-1,3 hydrocarbons, one of which is 2,3-dimethyl butadiene-LB, and an alpha methylene nitrile.

Copolymers of butadiene-1,3 hydrocarbons such as butadiene-1,3 and isoprene, with alpha methylene nitriles such as acrylonitrile and methacrylonitrile are well known and because they possess, in addition to the essential properties of natural rubber such as elasticity and vulcanizability with sulfur, other properties in which natural rubber is deficient such as resistance to oils, to oxidation and to aging, have been widely used as replacements for natural rubber in many applications. Such copolymers, however, are notoriously difiicult to process, one of the most troublesome processing difficulties being due to the fact that such materials become dry and tend to crumble when worked on a hot mill. Accordingly, it is necessary to carry out the milling operation on a relatively cold mill, to provide some means for dissipating the heat produced during milling and for maintaining a low temperature throughout the operation, and to employ much smaller batches of material than are ordinarily used with natural rubber, all of which expedients are highly undesirable from the standpoint of maximum processing efficiency, economy and speed.

I have now discovered that rubber-like copolymers made by the polymerization in aqueous emulsion of a mixture containing three or more components including at least two butadiene-1,3 hydrocarbons, one of which is 2,3-dimethyl butadiene-1,3, and an alpha methylene nitrile, in contrast to the above described two component copolymers, are easily processed and may readily be masticated on a hot mill. In addition such materials possess other desirable properties, such as high tensile strength and elongation, excel- 'lent oil resistance, abrasion resistance, heat resistance and resistance to aging, which are equal to and in some cases better than those of the two component copolymers.

In order to obtain these desirable copolymers it is necessary that the monomers polymerized be present in certain rather definite proportions. Thus the monomeric mixture must contain at least 50% by weight of two or more butadiene- 1,3 hydrocarbons, one of which present in at least by weight is 2,3.-dimethyl butadiene- 1.3, and at least 15% by weight of an alpha methylene nitrile. It is desirable that the mixture contain no polymerizable materials other than butadiene-1,3 hydrocarbons and alpha methylene nitriles but, if these materials are methylene group (Cl-12:) attached to a carbon atom adjacent to a nitrile group-(-CEN), such as acrylonitrile, alpha-methacrylonitrile, alphaethacrylonitrile, alpha-isopropacrylonitrile, a1- pha-methoxy-methacrylonitrile, alpha chloroethacrylonitrile, etc.

The preferred synthetic rubbers of this invention are those prepared by the ,emulsion polymerization of a mixture of monomers consisting solely of butadiene-1,'3, 2,3-dimethyl butadiene- 1,3 and acrylonitrile, the proportion of 2,3-di methyl butadiene being at least 10% by weight, the combined proportion of butadiene-1,3 and 2,3-dimethyl butadiene-1,3 being at least 50% by weight and the proportion of acrylonitrile being from 25 to" 45% by weight. Moreover, it is preferable that there be a larger proportion of butadiene-LS than of 2,3-dimethyl butadiene- 1,3 present in the mixture. For example, mixtures containingfrom 10 to 40% by weight of 2,3-dimethyl butadiene-1,3, from 35to by weight of butadiene-1,3 and about 25% by weight of acrylonitrile or mixtures containing from 10 to 25% by weight of 2,3-dimethyl butadiene-1,3, from 30 to 45% by weight of butadiene-1,3 and about 45% by weight of acrylonitrile yield excellent synthetic rubbers.

In the practice of this invention the polymerization of these monomeric mixtures to form synthetic rubber is carried out in aqueous emulsion. In this procedure the mixture of monomers is emulsified in water by the use of a suitable emulsifying agent. A polymerization initiator to start the polymerization reaction, a polymerization accelerator or catalyst to speed up the reaction and a polymerization modifier to improve the quality of the product are preferably added and the emulsion is allowed to polymerize by continuously agitating the same at a temperature of about 20-60 C. for a time suflicient to complete the reactio about to 100 hours usually being required. The polymerization product which is obtained in form of an aqueous dispersion resembling natural rubber latex is then stabilized by the addition of an age resistor or antioxidant and is coas llated by the same methods used to coagulate natural rubber latex, for example, by addition of acid, alcohol or salts or by a combination of these methods. Washing and drying of the coagulum produces a crude synthetic rubber which may be milled and otherwise processed in the same manner as natural rubber.

The preferred emulsifying agent for use in the above process consists of a water soluble soap derived from a fatty acid containing between 10 and carbon atoms pre molecule, such soaps as the sodium or potassium salts of lauric, myristic, palmitic, oleic or stearic acids being quite suitable. It is in general desirable to employ an emulsifying solution containing some free fatty acid, that is an aqueous solution containing a fatty acid which has been 70 to 90% neutralized with alkali, but it is also or even solutions of soaps, containing free alkali. Moreover emulsiiying agents which produce emulsions havin an acid reaction such as salts of organic bases containing long carbon chains, for example, the hydrochloride of diethyiaminoethyloleylamine, trimethylcetylammonium methyl sulfate and the hydrochloride of the. diethylaminoethoxyanilide of oleic acid, as well as other emulsifying agents which may be used under alkaline, acid or neutral conditions such as sodium lauryl sulfate and sodium isobutyl naphthalene sulfonate, may also be employed.

Polymerization initiators which ma be used in l the emulsion polymerization process include per- 9 oxides such as hydrogen peroxide and benzoyl peroxide, per-salts such as ammonium persultate, sodium perborate, potassium persulfate, potassium percarbonate and the like and other type of initiators such as diazoaminobenzene, dipotassium diazomethane disulionate and triphenyl methylazobenzene. The preferred polymerization catalysts or accelerators are those which contain a small amount of a heavy metal compound which is added to the emulsion either in the form of a simple-ionizable heavy metal salt such as ferrous sulfate, cobalt chloride, nickel nitrate or the like, as disclosed in the copending application of William D. Stewart, Serial No. 379,712, filed Feb. 14,

1941, or in the form of a redox system comprismg a heavy metal in complex combination or otherwise associated with some other material such as sodium pyrophosphates', levulinic acid, glycine, cystine, beta-mercaptoethanoi, quebrachitol or cholesterol, as disclosed ing applications of William D. Stewart, Serial Nos. 379,713, to 379,717 flied Feb. 14, 1941. F017 meriz'ation modifiers which, as mentioned above,

possible to employ com-' pletely neutralized soaps I monomer mixtures may not be aqueous emulsion perature and/or which in some manner improve included in the emulsion to be polymerized. All of these added substances, however, are mentioned herein only to indicate that the best results are obtained when one or more of them are present, and it is not to be inferred that the polymerized in their absence. The broad scope of the invention, accordingly, contemplates any polymerization in of the monomeric mixtures of this invention regardless of whether or not such added substances are employed.v

In order to illustrate the preparation of the improved synthetic rubbers of this invention, mixtures of butadiene-1,3, 2,3-dimethyl butadiene- 1,3 and acrylonitrile were made up as follows:

A 10 'gram sample of each of these monomeric "mixtures was then emulsified with 25 cc. of a in the copendare also preferably present during the polymerization are usually sulfur containing organic compounds such as the dialhl dixanthogens, the higher tetralkyl thiuram mono-, di-, and polysulfldes, the 2-mercaptoalkylthiazoles and bisalkyl thiazyl-2 disulfldes.

Other polymerization initiators, catalysts, ac- 7 celerators and modifiers inaddition to those listed above as well as other substances variously known .as polymerization regulators, promoters, etc. which enable the polymerization to boostried out in a shorter-time and at a lower temthen sealed in glass ,tained, each of which myristic acid which had been neutralized with sodium hydroxide. Also included in each of the emulsions were 0.035 grams of hydrogen peroxide as a polymerization initiator and 0.03 g. of diisopropyl dixanthogen as a polymerization modifier. The emulsions were containers and agitated at a constant temperature of 30 C. for about 60 hours whereupon latex-like dispersions were ,ob-

when stabilized and coagulated yielded from 9.5 to 10.0 grams of a rubber-like three component copolymer of hutadiene, dimethyl butadiene and acrylonitrile. All of these copolymers were coherent and plastic and when sheeted out on a two roll mixing mill it was observed that they could be milled readily at temperatures much higher than 1. without becoming dry and crumbling from the rollers. Two component polymers prepared in identically the same manner from 75 parts by weight of butadieneand 25 parts by weight of 2% aqueous solution of .acrylonitrile or 65 parts by weight of butadiene Itistobeunderstoodthattheabovespeeidc embodiments of this invention have been cited for illustrative purposes only and that it is not intended that the invention be limited solely thereto, for many modifications in accordance withthebroaddisciosurewiilbeapparentto thoseskilledintheartandarewithinthesplrit and scope of the appended claims.

I claim:

1. The process which comprises polymer-ism: in

'theiormoianaeueousemulsionamixtmecontainins at least 50% by weishtof two dmerent butadiene-IB hydrocarbons, one of which is 2.3-

75 dimethyl butsdiene-lfi present in at least 10% cases and acrylonitriie, the pr portion of 2,3-dimethyl butadiene-l,3 being at least by weight, the combined proportion of butadiene-l,3 and 2,3- dimethyl -butadiene-l,3 being at least 50% by weight and the proportion of acrylonitrile being from to 45% byweig'ht.

3. The process which comprises polymerizing in the form oi an aqueous emulsion a mixture containing butadiene-1,3, 2,3-dimethyl butadiene-l,3 and acrylonitrile, the proportion of 2,3-dimethyl butadiene-1,3 being at least 10% by weight, the combined proportion of butadiene-1.3 and 2,3-dimethyl butadiene-1,3 being at least 50% by weight, the proportion by weight of butadiene-l,3 being higher than that o! 2,3-dimethyl butadiene- 1,3 and the proportion of acrylonitrile being from 25 to 45% by weight. 4

4. The process which comprises polymerizing in the form of an aqueous emulsion a mixture containing from to 65% by weight of butadiene- 1,3, from 10 to by weight 01 2,3-dimethyl buttrile.

5. The process which comprises polymerizing in the form of an aqueous emulsion a mixture containing from 30 to by weight of butsdienel,3, from 10 to 25% by weight of 2,3-dimethyl but adieu-1,3 and about 45% by weight of acrylonk trile.

6. The process which comprises poLvmerizingin the form of an aqueous emulsion a mixture containing about by weight of butadiene-L3.

about 15% by weight or 2,3-dimethyl butadiene- 1,3 and about 25% by weight of acrylonitrile' 7. A synthetic rubber prepared by the method of claim 1.

8. A synthetic rubber prepared by the method of claim 2.

9. A synthetic rubber prepared by the method 7 01 claim 3.

10. A synthetic rubber prepared by the method or claim 4.

11. A synthetic rubber prepared by the method of claim 5.

12. A synthetic rubber prepared by the method of claim 6. 7

CHARLES I". FRYLING.

serene-1,: and about 25% b weightor mum-- 

